class_docstr: Velocity feature extractor.
  
  Extracts histograms of optical flow magnitude and direction.
  
  Args:
      n_bins (int): Number of direction bins used for the feature histograms.
code: def __init__(self, n_bins: int = 8) -> None:
      super().__init__()
  
      self.n_bins = n_bins
  
imports: from __future__ import annotations
  from enum import Enum
  import torch
  from torch import Tensor, nn
  from torchvision.models.detection import KeypointRCNN_ResNet50_FPN_Weights, keypointrcnn_resnet50_fpn
  from torchvision.models.detection.roi_heads import keypointrcnn_inference
  from torchvision.ops import roi_align
  from torchvision.transforms import Normalize
  from anomalib.models.ai_vad.clip import clip
label_desc: Use image node_id 1 to create a new VelocityExtractor object from inherited base classes: nn with example: obj = VelocityExtractor(n_bins)